Internal combustion engines are provided with a crankshaft, the output of which powers the vehicle drive train. As internal combustion takes place, the pistons are, during the power stroke, imposing pulses of torque upon the crankshaft. In some engines the piston firing torque impulses may be uneven or intermittent resulting in vibration in crankshaft, drive train and in the vehicle containing the internal combustion engine.
Certain internal combustion engines such as twin cylinder motorcycle engines and the like, may be particularly susceptible to piston firing torque impulse related vibrations. For example, and with particular pertinence to the present invention, most twin cylinder engines, especially the engines known as "V-twin" engines, manufactured by Harley-Davidson Motorcycle Company, Inc. have an intermittent or uneven cylinder filing sequence causing vibration relating to the torque impulses. In the foregoing engine during the 360 degree rotation of the crankshaft, the power strokes of the piston during cylinder firing occur approximately 80 degrees apart with the exhaust, intake and compression strokes encompassing the remaining 280 degrees. Accordingly, it can be seen that the crankshaft observes intermittent piston firing torque impulses during a 360 degree rotation.
By way of further background, the V-twin engines described above include a drive sprocket meshing with a chain which is driven by the drive sprocket, the chain meshing with a transmission input sprocket providing input to the motorcycle transmission. The crankshaft passes through the drive sprocket and is coupled to a device referred to as a compensator. The compensator is thereafter mated to the drive sprocket. The compensator is adapted during engine acceleration to prevent the heavy drive chain from slapping within the housing. The device is not sufficiently adapted to suppress vibrations relating to firing impulse torques.
In regards to automobile engines, it has been known in the prior art to provide a vibration dampening device at the end of the crankshaft opposite the drive train to dampen torsional vibrations. These dampeners are not well suited for installation such as in the V-twin engines referred to above particularly in a manner to cooperate with existing components thereof.